Several laboratories also list a correction factor for race when estimating renal function. This is despite the fact that the multidisciplinary guideline and the NHG Standard for Chronic Kidney Damage have not made any mention for several years that the patient’s origin should be taken into account when assessing renal function.
It concerns the result of the estimated kidney function, the estimated glomerular filtration rate (eGFR). The muscle mass composition of the patient plays a role in the interpretation of this eGFR. Some labs state in the results that the origin of the patient should be taken into account. For example, Erasmus MC mentions the sentence: ‘For patients with an African-Caribbean ethnicity, the result should be multiplied by 1.159.’ Until this week, the Amsterdam UMC also had the addition to take ‘Sub-Saharan descent’ into account. Peripheral hospitals such as Slingeland Hospital, SKB Winterswijk and Unilabs also have such a statement on their website. It is not clear how many laboratories do this, because not every laboratory has information about the determinations on their website. Ron Gansevoort, internist and co-author of the multidisciplinary guideline Chronic kidney damage, is surprised by this. ‘I don’t think it is conscious policy that the correction factor is still mentioned, but that should be removed.’
Since 2018, the NHG Standard and the multidisciplinary guideline Chronic kidney damage both recommend using the so-called CKD-EPI formula (chronic kidney disease epidemiology collaboration) to determine the eGFR. This formula is designed for adults and estimates kidney function based on average muscle mass for their height, weight, gender and age. This formula replaced the so-called MDRD formula (modification of diet in renal disease) that was still recommended in the predecessor of the current guidelines, the National Transmural Agreement on Chronic Kidney Damage from 2009. That MDRD formula contained the addition that a ‘black race’ had to be multiplied by a factor of 1.21. However, the CKD-EPI formula developed by the United States in 2009 turned out to be more accurate than the MDRD formula, and the guideline was therefore adjusted accordingly in 2018. This CKD-EPI formula also included a correction factor for ‘blacks’, namely a multiplier of 1.159, because the underlying US study found a difference between black and white participants.
Co-author of the multidisciplinary guideline Ron Gansevoort explains: ‘As a working group, when adopting the CKD-EPI formula, we extensively discussed whether we should also include the multiplication factor for race in the Netherlands. But in the Netherlands, the black population is very diverse in terms of physique, and in our opinion not essentially different from the physique of the non-black population. We therefore decided not to include the correction factor. Incidentally, the US has also abandoned that factor since 2021.’
The current aforementioned guidelines only report that large deviations in muscle mass compared to the average for age and sex and large deviations in body surface area can lead to an overestimation or underestimation of kidney function. The race or ethnicity factor is not mentioned in this context.
Apart from the fact that the formula is not applicable to the Dutch population, it also contributes to maintaining the image that there are biological differences between races, argued sociologist Alana Helberg-Proctor in an article in Medisch Contact in 2019. In addition, when the factor is applied, the kidney function may appear to be better than it actually is, as a result of which the degree of kidney damage is underestimated, for example. It is not well known whether this will happen, because the requesting physician must actively apply the correction factor. Ron Gansevoort: ‘In any case, the factor is not automatically processed in the results by the clinical chemistry laboratory, as was the case in the United States.’
The Amsterdam UMC has since removed the sentence after questions from Medisch Contact. Nephrologist Marlies Reinders and clinical chemist Christian Ramakers of Erasmus MC give the following reason for still mentioning the factor: ‘The discussion about which formula should be used took place recently. Both Erasmus MC departments support the consensus to use the CKD-EPI 2009 without the correction for race.’ Nevertheless, Erasmus MC indicates that it still intends to omit the correction factor from the standard eGFR. Reinders and Ramakers refer to a discussion that appeared this year in two different journals of the European Renal Association (with Gansevoort as first author), and the European Federation of Clinical Chemistry (EFLM).
However, both articles state that it has never been recommended for the CKD-EPI formula in Europe to apply a factor for race. However, both papers address the question of which CKD-EPI formula should be used. The US has recently implemented another, the so-called 2021 CKD-EPI, in which race no longer occurs. Gansevoort: ‘However, the advice for Europe is to maintain the old formula from 2009, partly because it seems to be better in the European population for estimating kidney function and for predicting the decline in kidney function.’